Muscles of the upper limb are typically divided in two large groups: muscles of the shoulder region and muscles of the free upper limb (or free upper extremity).

The muscles of the free upper limb may further be subdivided into upper arm muscles, forearm muscles, and hand muscles.

Shoulder muscles

The shoulder muscles include the following:

• Deltoid
• Supraspinatus
• Infraspinatus
• Teres minor
• Teres major
• Subscapularis

The most important of these are the four rotator cuff muscles - the subscapularis, supraspinatus, infraspinatus, and teres minor. These muscles connect the scapula to the humerus and provide support for the glenohumeral (shoulder) joint.

Upper arm muscles

The muscles of the upper arm are separated into two compartments by layers of fascia, bones, and ligaments:

• Anterior (flexor) compartment
• Posterior (extensor) compartment

The anterior compartment of the upper arm is separated from muscles of the posterior compartment by the humerus and by medial and lateral intermuscular septa. These septa are continuous with the deep fascia enclosing the arm and attach to the sides of the humerus. The anterior compartment contains the following muscles:

• Biceps brachii
• Brachialis
• Coracobrachialis

The posterior compartment of the upper arm is separated from the anterior compartment by the humerus and by the medial and lateral intermuscular septa. The muscles included into the posterior compartment are:

• Triceps brachii
• Anconeus

Forearm muscles

Similarly to the muscles of the upper arm, muscles in the forearm (lower arm) are also separated into several compartments by layers of fascia, bones, and ligaments:

• Anterior (flexor and pronator) compartment
• Lateral compartment
• Posterior (extensor and supinator) compartment

Hand muscles

Finally, the muscles of the hand may be categorized into three groups:

• Lateral group (muscles of the thumb)
• Middle group of hand muscles
• Medial group (muscles of the little finger)